St.MARTIN’S ENGINEERING COLLEGE - SMECsmec.ac.in/sites/default/files/lab1/MMS MANUAL LAB.pdfSTUDY OF MICROSTRUCTURE OF SOME NON- FERROUS ALLOYS 36 7. JOMINY END QUENCH TEST 42 Metallurgy

St.MARTIN’S ENGINEERING COLLEGE

DEPARTMENT OF MECHANICAL ENGINEERING

LAB MANUAL

METALLURGY AND MATERIAL SCIENCE

LAB

(II B.Tech I Sem)

(2016-17)

Document No:

SMEC/ME/LAB/MANUAL/MMS

DATE

OF

ISSUE: 01/07/2016

COMPLIED

BY: Mr.M.B.Naik

AUTHORISED

BY

Mr.D.V.SRIKANTH

MECH (HOD)

Metallurgy and material science Laboratory Manual II MECH

I Sem

LIST OF EXPERIMENTS ` Page No

1. SPECIMAN PREPARATION FOR METALLOGRAPHIC

EXAMINATION AND STUDY OF METALLURGYCAL

MICROSCOPE 3

2. STUDY OF MICROSTRUCTURE OF NON FERROUS

METALS 8

3. STUDY OF MICROSTRUCTURE OF CAST IRONS 10

4. PREPARATION AND STUDY OF MICROSTRUCTURE OF

MILD STEELS, LOW CARBON STEELS,

HIGH CARBON STEEL 14

5. STUDY OF MICROSTRUCTURE OF ALLOY STEELS 24

6. STUDY OF MICROSTRUCTURE OF SOME NON- FERROUS

ALLOYS 36

7. JOMINY END QUENCH TEST 42


I Sem

EXPERIMENT-1 ACCORDING TO JNTU SYLLABUS

SPECIMEN PREPARATION FOR METALLOGRAPHIC EXAMINATION AND

STUDY OF METALLURGICAL MICROSCOPE

1. AIM: a) To prepare the given specimen for metallographic examination.

b) To study the constructional details of Metallurgical Microscope and observe the micro

structure of the prepared specimen.

2. APPARATUS AND MATERIALS REQUIRED: Metallurgical microscope, emery belt, 1/0, 2/0, 3/0, 4/0 emery papers, lapping cloth, alumina

powder, etchants, sample of metal.

3. THEORY: The microstructure of metal decides its properties. An optical microscope is used to study the

microstructure. A mirror polished surface of the metal is required for metallographic study.

4. PROCEDURE OF SPECIMEN PREPARATION:

a) Cut the specimen to the required size (small cylindrical pieces of 10 to 15mm diameter with

15mm height (Or) 10mm cubes)

b) The opposite surfaces (circular faces in case of cylindrical pieces) are made flat with

grinding or filling. A Small chamfer should be ground on each edge for better handling. (If the

sample is small it should be mounted)

c) Belt grinding: One of the faces of the specimen is pressed against the emery belt of the belt

grinder so all the scratches on the specimen surface are unidirectional

d) Intermediate polishing: - The sample is to be polished on 1/0, 2/0, 3/0, 4/0 numbered emery papers with Increasing fineness of the paper. While changing the polish paper, the sample is to

be turned by 900

so that New scratches shall be exactly perpendicular to previous scratches.

e) Disc polishing (fine polishing):- After polishing on 4/0 paper the specimen is to be polished

on disc Polishing machine (Buffing machine). In the disc-polishing machine a disc is rotated

by a vertical shaft. The disc is covered with velvet cloth. Alumina solution is used as abrasive.

Alumina solution is sprinkled Continuously over the disc and the specimen is gently pressed

against it. In case of Non-ferrous metals Such as Brass, Brass is used instead of Alumina and

water. The polishing should be continued till a Mirror polished surface is obtained.

f) The sample is then washed with water and dried.

g) Etching:- The sample is then etched with a suitable etching reagent, detailed in article 5.


I Sem

h) After etching the specimen should be washed in running water and then with alcohol and

then finally dried.

i) The sample is now ready for studying its microstructure under the microscope.

5. ETCHING: Except for few cases a polished metallic surface can’t reveal the various constituents (phases).

Hence specimen should be etched to reveal the details of the microstructure i.e. a chemical

reagent should be applied on the polished surface for a definite period of time. This reagent

preferentially attacks the grain boundaries revealing them as thin lines. Thus under the

microscope the grain structure of the metal becomes visible after etching i.e. grain boundary

area appears dark and grains appear bright. The rate of etching not only depends on the

solution employed and composition of the material but also on the uniformity of the material.

A few etching reagents, their composition and their application are given below.

Sl.No

Name of Etchant

Composition

Application

1

2

3

4.

5.

6.

7.

8.

9.

Nital

a) 5% Nital

b) 2% Nital

Picral

Marbel’s reagent

Murakami’s reagent

Sodium hydroxide

Vilella’s reagent

Kellers reagent

Ammonium persulphate

Solution

FeCl3 solution

Nitric. acid (5ml) and

Abs. Methyl alcohol (95ml)

Nitric acid (2ml) and

Abs. Methyl alcohol (98ml)

Picric acid (4gm) and

Abs ethyl alcohol (96 ml)

Copper sulphate (4 gm),

Hydrochloric acid (20ml) and

water (20ml)

Potassium ferri cyanide,

(10grms), KOH (10grms) and

water (100ml).

Sodium hydroxide (10gm) and

water(90ml)

Hydro fluoric acid (20ml),

Nitric acid (10ml) and

Glycerene (30ml).

Hydro fluoric acid (1 ml),

Hydro chloric acid (1.5 ml),

Nitric acid(2.5 ml) and

Water (95 ml).

Ammonium persulphate (10gm)

And Water(90ml)

FeCl3 (5gm),

HCl acid (2ml) and

Ethyl alcohol (96ml)

General structure of iron

and steel


and steel


and steel

Stainless steels

Stainless steels

Aluminium alloys

Aluminium & its alloys

Duralumin

Copper and copper

alloysBrass


I Sem

6. METALLURGICAL MICROSCOPE: Metallurgical microscope is used for micro and macro examination of metals. Micro

examination of specimens yields valuable metallurgical information of the metal. The absolute

necessity for examination arises from the fact that many microscopically observed structural

characteristics of a metal such as grain size, segregation, distribution of different phases and

mode of occurrence of component phases and non metallic inclusions such as slag, sulfides

etc., and other heterogeneous condition (different phases) exert a powerful influence on

mechanical properties of the metal. If the effect of such external characteristics on properties

or the extent of their presence is known, it is possible to predict as to how metal will behave

under gone by the metal. Study of structure of metals at magnifications ranging from 50X to

2000X is carried out with the aid of metallurgical microscope.

A Metallurgical microscope (shown in fig) differs with a biological microscope in a manner by

which specimen of interest is illuminated. As metals are opaque their structural constituents are

studied under a reflected light. A horizontal beam of light from an appropriate source is directed

by means of plane glass reflectors downwards and through the microscope objective on to the

specimen surface. A certain amount of this light will be reflected from the specimen surface and

that reflected light, which again passes through the objective, will form an enlarged image

of the illuminated area. A microscope objective consists of a number of separate lens

elements which are a compound group behave as positive and converging type lens system of an

illuminated object. Specimen is placed just outside the equivalent front focus point of objective. A

primary real image of greater dimension than those of object field will be formed at some distance

beyond the real lens element. Objective size of primary image w.r.t object field will depend on

focal length of objective and front focus point of objective. By appropriately positioning

primary image w.r.t a second optical system, primary image may be further enlarged by an

amount related to magnifying power of eyepiece. As separation between objective and

eyepiece is fixed at same distance equivalent to mechanical tube length of microscope, primary

image may be properly positioned w.r.t eye piece. By merely focusing microscope i.e. increase or

decrease the distance between object plane and front lens of objective the image is located at

focal point. Such precise positioning of primary image is essential in order that final image

can be formed and rendered visible to observer when looking into eyepiece. If now entrance

pupil of eye is made to coincide with exit pupil of eyepiece, eyepiece lens is in conjunction with

cornea lens in eye will form a second real image on retina. This retrieval image will be erect, un

reversed owing to the manner of response of human brain to excitation of retina. The image since

it has no real existence, known as virtual image and appears to be inverted and reversed with

respect to object field6.1 Principle:

.

6.1.1. MAGNIFICATION: The total magnification is the power of objective multiplied by power of eyepiece (Power of

eye piece) (Distance from eye piece to object) / Focal length of object The magnification is

marked on the side of objective.6.2 CONSTRUCTION:


I Sem

The microscope consists of a body tube (refer Fig 1.1), which carries an objective below, and an eyepiece above with plane glass vertical illuminator immediately above the objective.

Incident light from a source strikes illuminator at 450, part of which is reflected on to the

specimen. Rays after reflection pass through the eye again. Working table is secured on heavy base. The microscope has compound slide to give longitudinal and lateral movements by accurate screws having scale and venires. Vertical movement of specimen platform is made by a screw to proper focusing. For getting perfect focusing fine adjustment of focusing can be made use of.

6.2.1. Light filters: These are used in metallurgical microscope and are essentially of three

types

a. Gelatin sheets connected between two planes of clean glass

b. Solid glass filters

c. Liquid dye solution

Solid glass filters are more preferable as they are more durable. Usually light filters are used

principally to render a quality of illumination. Hence filters improve degree of resolution.

A METZ - 57 model microscopes is used in the laboratory.

6.2.2 Optical compilation: Eye pieces and objectives of different magnifications are available.

Huygens eyepieces: 5X, 10X

Achromatic objectives: 5X, 10X, 45X

7. PRECAUTIONS:

a. Ensure mirror polished surface of specimen before etching.

b. Fine focusing should be done only after correct focusing has been done.

c. The glass lens should not be touched with fingers.

8. RESULT: Hence prepared a specimen for metallographic examination


I Sem

9. REVIEW QUESTIONS: i. What is the use of micro structural study?

ii. What is the difference among 1/0, 2/0, 3/0 and 4/0 emery papers?

iii. What is lapping?

iv. What are the different abrasives used in lapping?

v. Why the specimen has to be etched before micro structural study?

vi. What is the etchant used for brass?

vii. What is the etchant used for mild steel?

viii. In a microstructure how the gain boundary area appears?

ix. Why specimen is to be rotated through 90(between polishing on 1/0 and 2/0 emery papers?

x. What is etching reagent used for duralumin?

xi. Why should a specimen be prepared following the set procedure before its observation

under a microscope?

xii. Is the specimen preparation necessary at all? If so why? If not why not?

xiii. What is the difference between Metallurgical microscope and Biological microscope?

xiv. What is the magnification of the microscope?

xv. What are the different magnifications available in the microscope of our laboratory?

xvi. What are the precautions to be observed while studying, microstructure under

microscope?

xvii. What is the use of light filters?

xviii. How do you calculate the magnifying power of a microscope?

7


I Sem

EXPERIMENT-2: ACCORDING TO JNTU SYLLABUS

STUDY OF MICROSTRUCTURES OF NON FERROUS METALS

1. AIM: To determine the phases present and to draw the microstructure of Copper, Aluminium

& Magnesium.

2. APPARATUS AND SPECIMENS REQUIRED: Metallurgical microscope, Specimens of Aluminum, Copper and Magnesium.

3. THEORY: 3.1 INTRODUCTION TO NON FERROUS METALS Non ferrous metals don’t contain iron as base. A wide range of non ferrous metals are

employed for various engineering applications. Most Non ferrous metals posses good

corrosion resistance, formability, cast ability and special electrical and magnetic properties.

Important Non-ferrous metals, their melting points and crystal structures are tabulated here

under.

S.No Name

1. Aluminium (Al)

2. Antimony (Sb)

3. Bismuth (Bi)

4. Cadmium (Cd)

5. Chromium (Cr)

6. Copper (Cu)

7. Gold

8. Lead

9. Magnesium (Mg)

10. Manganese

11. Nickel (Ni)

12. Silver (Ag)

13. Tin (Sn)

14. Zinc

8

Melting point Degrees

C 660

630

271

321

1900

1083

1064

327

650

1250

1453

961

232


I Sem

The microstructure of following specimen are studied in this experiment.

a. Copper: Specimen : Pure Copper

Heat treatment: Nil

Etchant : Ferric chloride solution

Etching time : 100 seconds

The micro structure shows equi axed grains of copper.

b. Aluminium: Specimen :

Heat treatment: Etchant :

Etching time :

Pure Aluminium

Nil Ferric chloride solution 60 seconds

The micro structure shows grains of Aluminium.

c. Magnesium: Specimen :

Heat treatment: Etchant :

Etching time :

Magnesium

Nil Ferric chloride solution 60 seconds

The micro structure shows grains of magnesium.

5. RESULT: Hence drawn the microstructure of copper

6. REVIEW QUESTIONS: i. What are the important properties of Non-Ferrous metals and alloys?

ii. List out some important Non-Ferrous metals?

iii. What is melting point temperature of Aluminium?

iv. What is the crystal structure of Magnesium?

v. FCC metals are usually ductile and have high strain hardening tendency. Explain why?


I Sem

: EXPERIMENT-No.3: ACCORDING TO JNTU SYLLABUS

PREPARATION AND STUDY OF MICROSTRUCTURES OF CAST IRONS

1. AIM: To identify the different phases and to draw the microstructures of different cast irons.

2. APPARATUS AND SPECIMENS REQUIRED: Metallurgical microscope, specimens of different cast irons

3. THEORY: Cast irons are Iron carbon alloys in which carbon content varies from 2 to 6.67%. Cast irons

that contain carbon percentage between 2 to 4.3% it is called hypo eutectic cast iron. If corbon

content of cast iron is 4.3% it is called as eutectic cast iron. If the carbon content is above 4.3%

it is called Hyper eutectic cast iron.

3.1 Cooling of a Hypo eutectic cast iron (3% carbon): Alloy 4 in fig. (Iron – Iron carbide equilibrium diagram) represents Hypo eutectic castiron with 3% carbon. Initially at point X1 the alloy is in completely liquid state as shown in

fig.5.1a. As it is slowly cooled no change is observed until it crosses ‘BC’ line (liquidus line). After crossing ‘BC’ line austenite dendrites start forming from liquid iron. At X2 the

microstructure of alloy shows dendrites of proeutectoid austenite in liquid iron as shown in fig.5.1b. On further cooling of alloy when it crosses ‘ECF’ line (eutectic temperature line)

liquid of alloy undergoes eutectic reaction at constant temperature (11300C) and transforms

into lideburite (eutectic mixture of austenite and cementite)

Liquid eutectic cast iron (Austenite + Cementite) (lideburite) The microstructure of alloy at X3 consists of dendrites of primary austenite, eutectic

austenite and Cementite as shown in fig.5.1c. On further cooling of alloy there is no

considerable change in Microstructure except increase of cementite (This cementite isseparated

from austenite because of Decrease of solubility of carbon in austenite as temperature is

reduced). On further cooling of alloy when ‘PSK’ line (eutectoid temperature line) is crossed the austenite (Primary as well as eutectic) undergoes eutectoid reaction at constant temperature

(7230C) and is Converted to pearlite. At X4 the microstructure of alloy consists of dendritic

areas of transformed Austenite (i.e. pearlite) in the matrix of transformed lideburite (pearlite+cementite).

3.2 Cooling of Eutectic cast iron (4.3% carbon): Alloy 5 in fig. represents eutectic castiron with 4.3% carbon. Initially at X1 the alloy is

completely in liquid state as shown in fig.5.2a. On further cooling of the alloy no change is observed until crosses ‘ECF’ (eutectic temperature line) at C. At ‘C’ liquid iron undergoes

eutectic reaction at constant temperature (11300C) and transforms into lideburite. At X2 the

alloy consists of completely lideburite (Austenite + Cementite) as shown in fig.5.2b. On further cooling of alloy no change is observed till it crosses ‘PSK’ line. When alloy crosses eutectoid temperature line (‘PSK’) eutectic austenite


I Sem

Undergoes eutectoid reaction at 7230C and transforms into pearlite. The microstructure of

alloy at X3 (just below ‘PSK’ line) consists of transformed austenite (pearlite and cementite) on

further cooling of alloy to room temperature there is no change in the microstructure.

3.3 Cooling of Hyper eutectic cast iron (4.5% Carbon) Alloy 6 in fig.2.5 represents Hyper eutectic castiron with 4.5% carbon. Initially at X1 the alloy

consists of only liquid iron as shown fig.5.3(a). On cooling of alloy no change is observed till it crosses ‘CD’ line. After crossing ‘CD’ line cementite starts nucleating from liquid iron. The microstructure of alloy at X2 consists of proeutectic cementite dendrites in liquid iron as shown

in fig.5.3b. On further cooling of alloy no change is observed till it crosses ‘ECF’ line (eutectic temperature line). When ‘ECF’ line is crossed liquid of alloy undergoes eutectic reaction at

constant temperature (11300C) and is transformed into lideburite (eutectic mixture of austentite

and cementite). The microstructure of alloy at X3 (just below ‘ECF’ line) consists of eutectic

austenite, cementite and proeutectic cementite as shown in fig.5.3c. On further cooling of alloy no change is observed till it crosses ‘PSK’ line (eutectoid temperature line). When it crosses

‘PSK’line the austenite of alloy undergoes eutectoid reaction at constant temperature (7230C)

and transforms into pearlite. At X4(just below ‘PSK’ line) the microstructure consists of

cementite and pearlite as shown in fig. The alloy is further cooled to room temperature there is no change in the microstructure.


I Sem

3.4 The useful properties of cast iron are i) Good fluidity(ability to fill narrow cavities in castings in liquid steel) ii) Low melting point

iii) Good machinablity iv) Less dimensional changes during solidification.

Cast irons are brittle and have low tensile strength than most of the steels. Specially in the case

of Grey cast iron, the graphite present will act like cracks and reduce tensile strength, toughness

etc.,

Types of cast irons: Depending on the form of carbon, cast irons are divided into

a) White cast iron b) Gray cast iron c) Malleable cast iron d) Speheroidal cast iron

e) Chilled cast iron

3.5a White cast iron: In white cast iron most of the carbon is present in combined form as cementite. This is obtained

by rapidly cooling the cast iron from its molten state. These are hard and hard and wear

resistant. These are used only for hard and wear resistance applicarions and also used as raw

material to produce malleable iron. At room temperature microstructure of Hypi eutectic C. I

consists of dendritic areas of transformed austenite in a matrix of transformed lideburite. At

room temperature microstructure of eutectic cast iron consists of cementite and pearlite. At

room temperature microstructure Hyper eutectic cast iron consists of cementite and pearlite. At

room temperature microstructure Hypereutectic C.I consists of dendrites of primary cementite

in the matrix of transformed lideburite.

3.5b Grey cast iron: In Grey cast iron carbon is present as free graphite flakes. They contain more carbon and

silicon content than white cast irons. It is a low melting alloy having good castability and good

damping capacity. The tendency of carbon to form graphite flakes is due to increase in carbon

and silicon content and decreasing the cooling rate. Grey cast iron receive its name from the

color of a freshly made fracture. At room temperature the microstructure of Grey cast iron

consists of graphite flakes and pearlite.

3.5c Malleable cast iron; Malleable cast iron is produced by heating white cast iron to 900 to 1000

0C for about 50 hours

followed by slow cooling to room temperature. On heating white cast iron, cementite structures

tend to decompose into ferrite and tempered carbon. The lubrication action of graphite imparts

high Machinability to malleable cast iron. Malleable castings are tough, strong and shock

resistant. These are used for wide range of applications such as automobile parts, railroad

equipment, man hole covers etc., and at room temperature the microstructure of Malleable cast

iron consists of rosettes of tempered carbon graphite in the matrix of pearlite.

3.5d Spheroidal graphite cast iron (Nodular cast iron or Ductile cast iron):

Spheroidal graphite cast iron is an iron carbon alloy having a structure composed of nodules

(spheroids) of graphite formed directly during the process of solidification and embedded in

matrix of steel. The formation of spherical graphite is due to addition of magnesium for hypo

eutecthic cast iron and cerium for hyper eutectic cast iron. This is used for hydraulic cylinders,

values cylinder heads for compressor and diesel engine etc., Due to spherodization tensile

strength, ductility and toughness are improved. This cast iron combines the advantages of cast


I Sem

iron and steel. The graphite in spherical shape reduces stress concentration effect and hence

higher strength and toughness results.

3.5e Chilled cast iron: Chilled cast iron is produced by adjusting the composition of white cast iron and then cooling it

rapidly to room temperature. Rapid cooling promotes hard, thin layer on the surface of a soft

iron casting. It is used where surface hardness is important. It finds applications in making dies

and rolls for crushing.

4. The Micro structure of following cast irons are studied in this exercise

4.a Grey cast iron: Specimen : Grey cast iron

Composition : 3.5% carbon 2% silicon 0.5% manganese 0.4% phosphorous 0.09%

sulphur

Heat treatment : Nil

Etchant : Nital


The micro structure shows uniformly distributed and ranbomly oriented graphite flakes in the

matix of ferrite and pearlite.

Applications: These are widely used for machine bases, engine frames, cylinders and pistons of

I.C engines etc.,

b. White cast iron: Specimen : Composition :

Heat treatment :

White cast iron

4% carbon 0.5% silicon 0.4% manganese 0.05% phosphorous 0.3%

sulphur Nil

Etchant : Nital


The micro structure shows dendrites of transformed austenite (pear) in the matrix of

transformed Ledeberite(i.e. pearlite and cemenite). Majority of these cast irons are Hypo

eutectic cast irons.

Applications: Used for wearing plates, pump linears, dies, etc., and also for production of

malleable castings.

c. Malleable cast iron: Specimen : Malleable cast iron

Composition : 4% carbon 0.5% silicon 0.4% manganese 0.1% phosphorous 0.1%

sulphur


Etchant : Nital



I Sem

Applications: Cam shafts, Crank shafts, Axles, etc.

d. Speheroidal graphite cast iron (Nodular cast iron or ductile cast iron): Specimen : Ductile cast iron/Nodular/Spheroidal cast iron

Composition : 3.3% carbon 2.4% silicon 0.05% manganese small amount of Mn ,

phosphorous, sulphur


Etchant : Nital


The micro structure shows a typical structure. It contains nodules(spheroids) of graphite

surrounded by ferrite in the matrix of pearlite.

Applications: Used for gears, punches, dies, metal working rolls, furnace doors, etc.,

RESELT: Hence identify the different phases and drawn the microstructures of different cast iron.

5. REVIEW QUESTIONS: i. What are the different types of cast irons?

ii. What is the difference between White cast iron and Grey cast iron?

iii. What are the important properties of Grey cast irons?

iv. Why White cast iron has limited applications?

v. What is the structure of Malleable cast irons? Explain the heat treatment cycles used for

black heart and white heart malleable irons?

vi. What is the additional metal added for sperodisation for Hypo and Hyper eutectic cast

irons? How they act?

vii. What is Chilled cast iron?

viii. What is the difference between Ferritic malleable, Pearlitic malleable and Pearlitic-ferritic

malleable casr irons?

ix. Why Gray cast iron has got that name?

x. Why Gray cast iron is so brittle?

xi. Explain important roperties of different types of cast irons?


EXPERIMENT-No.3: DIFFERENT FROM JNTU SYLLABUS

1. The first lesson concentrates on the metallurgical microstructures of cast irons.

- The photomicrograph at below shows a grey cast iron at 100X. It has been etched

with Nital, as have all the other cast irons in this lesson.

Note that the eutectic graphite is arranged in rosettes here. This is a hypereutectic

composition.

What happened to the austenite ? Go back & look at the iron - carbon phase diagram

1. Grey cast iron

-

Answer: The austenite decomposed to ferrite plus graphite, and the graphite added

itself onto the graphite flakes that were already present. Faster cooling rates can allow

pearlite to form, or even martensite if the casting is quenched.

2. pearlitic grey cast iron

Here we have an example of a pearlitic grey cast iron, shown at 200X.

Cooling of the casting was rapid enough that the carbon rejected by the

decomposing austenite could not reach the graphite flakes. Therefore, pearlite

formed everywhere that the austenite was thereby retained, except where the

carbon was depleted by atmospheric oxidation.

Note the "flat" white appearance of the ferrite in the image at left compared to

the yellowish appearance of the iron - iron phosphide eutectic in the

photomicrograph below.

http://www.georgesbasement.com/Microstructures/CastIronsHighAlloySteelsSuperalloys/Lesson-1/Introduction.htm#Iron_carbon_phase_diagram


I Sem

Here the magnification is 500X, and there is an exaggeration of the volume fraction of

phosphide eutectic in this particular area, because this is the lowest freezing

microconstituent in this cast iron, and so it is concentrated in the last portions of the

casting that freeze.

3.Nodular cast iron


I Sem

The photomicrograph at below shows the rounded shapes of the graphite nodules at

100X. These shapes are typical in what is called ductile iron or nodular cast iron.

This structure is obtained by inoculating the melt just before pouring with an element

which changes the surface chemistry of the graphite. This element (usually magnesium)

reacts with surface active impurities (probably sulfur) so that the graphite can grow in a

direction perpendicular to the basal plane of the hexagonal graphite crystal structure. In

grey cast iron the graphite flakes grow edgewise.

Here you can see the rounded shape and internal microstructure of a graphite

nodule at 500X.

Think about the vast economic effect of obtaining these ductility enhancing nodules in castings without the prolonged annealing treatment required to

make malleable iron. The savings in energy more than cover the extra energy

needed to make the metallic magnesium (which is usually produced as

magnesium ferrosilicon).


I SEM


PREPARATION AND STUDY OF MICRO STRUCTURES OF

PLAIN CARBON STEELS

1. AIM To identify the different phases and to draw the microstructures of Plain Carbon Steels.

2. APPARATUS AND SPECIMENS: Metallurgical Microscope, specimens of plain carbon steel of different composition (un

treated)

THEORY: 3.1 Alloy:

Combination of two or more metals is called alloy. The substances that make the alloy are

called its components. The metals are mixed together in required proportion when they are in

molten form and then they are allowed to solidify together. After solidification the

components of alloy may be in the form of solid solution, chemical compound, mechanical

mixture.

If the constituents of the alloy are completely soluble in both liquid and solid state a solid

solution is formed. If constituents of the alloy are completely soluble in liquid state and

completely insoluble in solid state a mechanical mixture is formed.

3.1.1 Phase: A homogenous, physically distinct and Mec

Hanically separable part of the system under study is known as phase.

3.2 Cooling Curve: For a Molten metal that is cooled from molten state to room temperature the graph drawn

between time on X-axis and temperature on Y-axis is known as a cooling curve. A pure metal

solidifies at constant temperature.


I Sem

3.2. a. Cooling Curve of pure metal: Cooling curve of pure metal is shown in fig.. At ‘A’ metal is in liquid state. As metal is cooled

the solidification starts at ‘B’. As metal is further cooled the temperature of metal remains

constant but metal is converted from liquid state to solid state. Solidification is completed at

point ‘C’. From ‘C’ to ‘D’ there is no change in the solidified metal (except fall in

temperature).

3.2.b. Cooling curve of a solid solution: If the components of the alloy are completely soluble in both liquid and solid state a solid

solution is formed. Cooling curve of a solid solution is shown in fig.2.2. From ‘A’ to ‘B’ the

alloy is in liquid state. Solidification starts at ‘B’ and solidification ends at ‘C’. From ‘C’ to

‘D’ there is no change is solid state of alloy. From Fig.3.2 it can be observed that a solid

solution alloy is solidified over a range of temperature.

3.2. c. Cooling curve of an eutectic alloy: Cooling curve of a binary eutectic alloy is shown in fig.2.3. From ‘A’ to ‘B’ the alloy is in liquid state. As alloy is further cooled from ‘B’ the temperature of alloy remains constant, and two solids S1, S2 start separating out from the liquid separately. The alloy gets completely

solidified at ‘C’ and gives a mixture of S1 and S2 (eutectic mixture). From ‘C’ to ‘D’ there is

no change in the solidified alloy.

3.3 Cooling Curve of pure Iron: Cooling curve of pure Iron is shown in Fig. 2.4 Depending on the temperature Iron exists in

separate crystalline forms (α, γ, and δ). Above 15390C Iron is in liquid state. As Iron is cooled

from liquid state at 15390C all liquid is converted to δ – Iron. As it is further cooled upto

14000C Iron is in the form of δ – Iron and at1400

0C all δ – Iron is converted to γ- Iron. As the

Iron is still cooled from 14000C up to 910

0C Iron is in the form of γ- Iron and at 910

0C all γ-

Iron is converted to non magnetic α- Iron. If the Iron is further cooled from 9100C, at 768

0C

non magnetic α- Iron is converted to magnetic α – Iron. If the Iron is further cooled to room temperature Iron exists as magnetic α – Iron only.

3.4 Iron – Iron Carbide equilibrium diagram: Iron – Iron Carbide equilibrium diagram is shown in fig. Iron carbon alloys contain less than 2% carbon are called steels and iron carbon alloys that contains >2% Carbon are called cast irons. Steels having <0.8% Carbon are called Hypo eutectoid steels, 0.8% carbon are called eutectoid steels and >0.8% carbon are called Hyper eutectoid steels.

3.4.1 Curie temperature (7680C):

At Curie temperature on cooling Non-magnetic α – iron becomes magnetic. ABCD is the liquids line and AHJECF the solidus line of the system. (i.e. the alloy will be completely in liquid state at all temperature above liquids line and will be under solid state at all temperatures below solidus line).

3.4.2 Critical points: The temperature at which the transformation in solid state occurs are called critical points. In

hypo eutectoid steels GS (A3 line) and PS (A1 line) represents upper and lower critical points.


I Sem

In hyper eutectoid steels the line SE (Acm) and SK (A13) represents upper and lower critical

temperatures respectively.

3.4.3 Different phases that apperar in Fe-Fe3C diagram:

a. Ferrite (α): It is an interstitial solid solution of carbon in α – iron, maximum solubility of

carbon in α – iron is 0.025% at 723oC.

b. Austnite (γ): It is an interstitial solid solution of carbon in γ – iron, maximum solubility of

carbon in γ – Iron is 2% at 1130oC. c. Cementite (Fe3c): It is a chemical compound of iron and carbon that contains 6.67% carbon

by weight.

d. Pearlite: The eutectoid mixture of Ferrite and cementite is called Pearlite.

e. Lideburite: The eutectic mixture of austenite and cementite is called Lideburite the three horizontal lines in the diagram (HJB, ECF and PSK) indicate three isothermal reactions at

fixed composition and temperature.

3.5 Slow Cooling Hypo Eutectoid steel (0.18% Carbon): In fig, alloy 1 represents 0.18% carbon steel. Initially at X, the alloy is in completely liquid

state as shown in fig 3.6a. As it is cooled when it crosses ‘AB’ line δ – Iron neucli start forming in liquid Iron. The Micro structure of the alloy at X2 is shown in fig 2.6b. As alloy is

further cooled, when it crosses ‘BJ’ line at ‘J’ liquid Iron and δ – Iron are combined together

at constant temperature to form γ- Iron. This reaction is known as peritectic reaction.

Cooling

L + δ γ

(Liquid) + (δ - Iron) (Austenite)

If the alloy is further cooled at X3 the microstructure of the alloy consists of homogeneous

solid solution of γ – Iron as shown in fig. 2.6c. Upon slow cooling of alloy from X3 nothing

happens until ‘A3’ line ferrite begins to form at austenite grain boundaries. The micro structure

of alloy at X4 is shown in fig.2.6d. As cooling progresses amount of ferrite increases and

remaining austenite becomes richer in Carbon.

At X6 the Austenite gets converted into ferrite and cementite (a Mechanical mixture) at

constant temperature. This is known as eutectoid reaction.

δ Cooling

Austenite (Ferrite + Cementite) (pearlite)

The eutectoid mixture of ferrite and cementite is known as pearlite. At temperature just below

X6 the micro structure shows pearlite and proeutectoid ferrite as shown in fig.2.6f

On further cooling of the alloy to room temperature no more phase changes are observed.

Hence at room temperature microstructure shows pearlite and proeutectoid ferrite.

3.6 Cooling of Eutectoid Steel (0.8% Carbon):


I Sem

In Fig 2.5 alloy 2 represents 0.8% Carbon steel. Initially at X1 the alloy is completely in liquid

state as shown in fig.2.7a. On slow cooling once it crosses ‘BC’ line (liquidus line) γ- Iron dendrites start forming in the liquid Iron. At X2 alloy consists of γ – Iron dendrites in liquid

Iron as shown in fig.2.7b. As the cooling of alloy is continued more and more austenite is formed until it crosses ‘EJ’ line. At X3 the alloy consists of uniform solid solution of γ – Iron

as shown in fig 2.7c. On further cooling of alloy from X3 no changes is observed until it

crosses ‘PSK’ line (lower critical temperature line) at ‘S’. At point ‘S’ all the austenite present

in the alloy undergoes eutectoid reaction at constant temperature (7230C) and gets converted

into pearlite (mechanical mixture of ferrite and cementite).

Cooling

Austenite (Ferrite + Cementite) (pearlite)

Just below the eutectoid temperature line (‘PSK’) at X4 the alloy consists of 100% pearlite as

shown in fig. 2.7d. There is no change in microstructure on cooling of the alloy from X4 to room temperature.

3.7 Cooling of Hyper eutectoid steel (1% Carbon): In fig.2.5 ‘alloy 3’ represents 1% Carbon steel. Initially at X11, the alloy is completely in

liquid state as shown in fig.2.8a. On slow cooling from X1 no change is observed till ‘BC’ line

(liquidus line) is crossed. Once ‘BC’ line is crossed on further cooling of alloy to X2 austenite

crystals start neucleating from liquid Iron as shown in fig.2.8b.As cooling is continued more and more amount of austenite is formed. By the time it crosses the line ‘JE’ all liquid Iron is converted to austenite. At X3 the alloy consists of unform solid solution of austenite as shown

in fig2.8c. On slow cooling of alloy from X3 nothing happens until ‘Acm’ line is crossed at

X4. Above X4 austenite is an unsaturated solid solution. At X4 austenitie is saturated with

carbon. As the temperature is decreased carbon content of austenite (maximum amount of carbon that can be desolved in austenite) decreases along ‘ES’ line. So on cooling of alloy from X4 to X5 excess carbon is precipitated as cementite primarily along grain boundaries. The

micro structure of alloy from X5 is shown in fig.2.8d. On further cooling of alloy, once

temperature of alloy crosses lower critical temperature line(‘PSK’ line) at X7 the austenite

present in the alloy undergoes eutectoid reaction and gets converted into pearlite. Just below A3.1 line (‘SK’ line) at X7 the microstructure of alloy shows around 96% pearlite and

continuous network of cementite (around 4%) as shown fig 2.8e. 3.8 Plain Carbon Steels: The usual composition of plain carbon steel is as follows

Carbon 0.08 to 1.7%; Mn 0.3 to 1.0%; Silicon 0.05 to 0.3%; Sulphur 0.05 % (max);

Phosphorus 0.05% (max)

In plain carbon steels, carbon percentage plays a vital role in deciding the properties of steels.

Depending on the carbon percentage plain carbon steels are divided into three types.

a. Low carbon steel (Mild steel) b. Medium carbon steel c. High carbon steel

The microstructure of low carbon steel (Mild steel) consists of single phase ferrite, (equi axial

grains) i.e., it doesn’t respond much to the heat treatment. The properties don’t vary to any

treatment given to the mild steel. It remains mild.


4. The following specimens are to be studied for their Microstructure in this exercise

a. Mild steel:

Specimen

Composition

Heat treatment

Etchant

Etching time

: Mild steel

: Very low carbon (0.05%), remaining iron

: Nil

: Nital : 10 seconds

The structure is single phase equiaxed grains of ferrite.

Application: nuts, bolts, rivets, shafts etc.,

b. Hypo eutectoid steel:

Specimen : Hypo eutectoid steel

Composition : 0.5% carbon, remaining iron


Etchant : Nital

Etching : 10 seconds

The microstructure shows ferrite and pearlite.

c. Eutectoid steel:

Specimen : Eutectoid steel

Composition : 0.8% carbon, remaining iron


Etchant : Nital


The microstructure of eutectoid steel consists of 100% pearlite.

d. Hyper eutectoid steel:

Specimen : Hyper eutectoid steel (High carbon steel)

Composition : 1% carbon, remaining iron


Etchant : Nital


The microstructure shows continuous network of cementite along the gain boundaries

of coarse pearlite.

RESULT: Hence identified the different phases and drawn the microstructures of plain carbon

steel22


I Sem

REVIEW QUESTIONS:

1. What is a cooling curve?

2. What is the use of equilibrium diagram?

3. What is Curie temperature?

4. What is the percentage of carbon in cememtite? 5. What are the different phases in Fe- Fe3c equilibrium diagram?

6. How Cast iron and steel are distinguished with respect to carbon percentage?

7. What is eutectoid reaction?

8. What is eutectic reaction?

9. What is peritectic reaction?

10. What is peritectoid reaction?

11. Draw the microstructure of eutectoid steel?

12. Draw the microstructure of hypo eutectoid steel?

13. Draw the microstructure of hyper eutectoid steel?

14. What is the maximum solubility of carbon in ferrite?

15. What is the maximum solubility of carbon in Auestenite?

16. What are the properties & applications of mild steel?

17. What are the properties & applications of medium carbon steel (Hypo eutectoid steel)?

18. What are the properties & applications of Eutectoid steel?

19. What are the properties & applications of hyper eutectoid steel?



STUDY OF MICROSTRUCTURES OF ALLOY STEELS

1. AIM: To identify the different phases and to draw the microstructures of alloy steels.

2. APPARATUS AND SPECIMENS REQUIRED: Metallurgical microscope, specimens of different Alloy steels

3. THEORY: Steels are to be alloyed for improving their mechanical properties. Common alloying

elements are Al, Ni, Mn, Cr, etc., however, the properties of alloy steels are not so much

superior to plain carbon Steels in untreated condition. Different heat treatments are given to

alloy steels to fully exploit their Properties.

3.1 Effect of Alloying Elements: Alloying elements may have one or more of the following

effects.

a) Solid Solution Strengthening/Hardening: Most of the alloying elements are soluble

in ferrite to some extent and form solid solutions when added to steel. Solid solutions are

harder and stronger than the pure metals and hence these elements increase strength and

hardness of steels.

Examples: Mn, Cr, W, Mo, V, Ti, Ni, Si, Al, Zr………

b) Formation of carbides: Some of the alloying elements combine with carbon in steel

and form respective carbides. These alloy carbides are hard and increase wear and abrasion

resistance of steels.

Examples: Mn, Cr, W, Mo, V, Ti, Zr, and Nb………

c) Formation of Intermediate Compounds: Some of the elements form intermediate

compounds with iron.

Examples: Fe, Cr(sigma phase in high chromium alloys) and Fe3W2 (in tool steels).

d) Formation of inclusions: they may combine with oxygen and form oxides when

added to steel.

Examples: Si, Al, Mn, Cr, V, and Ti……

e) Shifting of critical temperature and eutectoid carbon: the alloying element may

lower or raise the transformation temperature of steel. Elements, which are austenite

stabilizers like Ni, and Mn, lower the eutectoid temperature (A) while the elements, which are

ferrite stabilizers, raise the above temperature.

Most of the alloying elements shift the eutectoid carbon to lower values e.g. the carbon

content of Eutectoid in a 12% Cr steel is less than 0.4% as against to 0.8% in plain carbon

steels.

f) Lowering of critical cooling rate: Most of the alloying elements (except Co) shift the

T.T.T diagram to the right side, thus decreasing the critical cooling rate. This effect is very

useful for increasing the hardenability.

g) Changes in volume during transformation: Elements may be chosen in proper

proportion sp as to reduce the volume change to reduce distortions and the risk of quench

cracking during hardening.


I Sem

h) Other effects: i) The transformation may become sluggish.

ii) The corrosion and oxidation resistance may increase e.g. chromium increases corrosion

resistance by forming a thin film of chromium oxide on the surface. This is found in stainless

steels.

iii) Creep strength may get increased due to the presence and dispersion of fine carbides.

iv) Fatigue strength may also get increased.

3.2 Classification of Alloying Elements: With respect to relation with Carbon, alloying elements can be classified into 3 groups.

a) Carbide forming elements: They form carbides when added to steels or cast irons.

Examples: Ti, Zr, V, Nb, W, Mo, Cr, Mn……

b) Neutral Elements: Cobalt is the only element in this category, which neither forms

carbides nor causes graphitization.

c) Graphitizing elements: They try to decompose the carbides into graphite, in cast irons.

Examples: Ni, Si, Cu, Al a) Austenite stabilizers: the elements from this group raiseA4, temperature and lower

A3temperature, thus increasing the range of stability of austenite

Examples: Mn, Ni, Cu, C, N………

b) Ferrite Stabilizers: These elements lower A4 temperature and raise A3 temperature, thus

increasing the range of stability of ferrite. Examples: Cr, W, Mo, V, Ti, Ni, Si, Al, Zr, B Nb, P……

3.3 Uses of Alloying Elements: a) Sulphur: Sulphur combines with iron and forms iron sulphide and induces brittleness

phase.

b) Phosphorus: Phosphorus dissolves in ferrite and increases its tensile strength and hardness.

c) Silicon: it is ferrite solid solution strengthener. It dissolves in ferrite increasing strength,

hardness and toughness without loss of ductility. It is a strong graphitizer in cast irons.

d) Manganese: It dissolves in ferrite and increases yield strength tensile strength, toughness

and hardness. It combines with Sulphur and forms MnS reducing the detrimental effect of

FeS.

e) Nickel: It is ferrite solid solution strengthener. It dissolves in ferrite and increases hardness,

tensile strength and toughness without decreasing ductility. It increases impact resistance of

steels at low temperature i.e. it reduces ductile-brittle transition temperature.

f) Chromium: Chromium has several functions as given below:

i) It increases hardenability of steels.

ii) It forms carbides and increases hardness and wear resistance of steels.

iii) It increases corrosion and oxidation resistance when added in substantial amount.

Chromium has following disadvantages

i) It makes the steel susceptible to temper embrittlement.

ii) These steels are liable to form surface markings, generally referred to as chrome

lines.


g) Tungsten: It as following functions:

i) It increases hardenability.

ii) It forms carbides and increases wear and abrasion resistance.

iii) It refines the gain size and the carbides inhibit the grain coarsening.

iv) It reduces the tendency of decarburization.

h) Molybdenum: Molybdenum has similar functions as Tungsten. However, its resistance to grain coarsening

and decarburization is less as compared to Tungsten.

i) Vanadium: The properties of vanadium containing steels are on similar lines as tungsten or/and

molybdenum containing steels. However, vanadium containing steels have improved distinct

properties as stated below.

i) The resistance to grain coarsening is excellent.

ii) The carbides of vanadium are extremely hard and hence, vanadium promotes

secondary hardening during tempering.

iii) It effectively improves the fatigue and creep resistance.

iv) It is strong deoxidizer.

j) Titanium: It is strong carbide former it effectively inhibits grain coarsening and also acts as

a grain refiner.

k) Cobalt: It is neither carbide former nor a graphitizer. It is the only element, which reduces

hardenability of steels.

l) Aluminium: It is a powerful deoxidizer and hence is used for killing of steels. It is a grain

refiner and also inhibitor.

m) Boron: Small additions of boron (0.001 – 0.003%) sharply increase hardenability of

medium carbon steels.

4. The microstructure of following Alloy steels are studied in this exercise

a. High Speed Tool Steel: The important characteristics of Tools steels are i) High hardness at eleveated temperatures ii) High wear resistance iii) High hardenbility iv) Good touhness.

These steels maintain high hardness up to a temperature about 5500C. These are designated by

T- Series. Specimen : High speed steel

Composition : 0.7%C, 18%W, 4%Cr, 1%V

Heat treatment: Heated to a temperature of 1250-13000C,

soaked at this temperature for very Short period of time. The steel is then quenched in oil to room temperature.


I Sem

Etchant : Nital


The microstructure consists of tempered martensite, alloy carbides and low carbon retained

austenite.

Applications : Cutting tools

b. Stainless steel: these steels have high corrosion resistance

specimen : Stainless steel(Austenitic)

Composition : <0.15%C, 18%Cr, 10%Ni

Etchant : Nital


The microstructure consists of Austenitic grains. The dark regions are due to alloy carbide

precipitation.

Applications: Utensils, Chemical plant equipment, Medical equipment Blades etc.,

c. High Carbon Chromium steel: These steels have very high hardenability and shows very

less distortion during hardening.

Specimen : High carbon high chromium steel

Composition : 1.5%C, 12%Cr, 1%Mo

Heat treatment : Hardened and tempered

Etchant : Nital


The microstructure consists of tempered martensite. The dark area are alloy carbides.

Applications: Drawing dies, Blanking dies etc.

En36: Specimen :

Composition :

En36

015%C, 0.6%Mn, 3.35%Ni, 1.1%Cr,0.35%Si

Heat treatment : Case carburising.

Etchant : Nital


The microstructure shows a white compound layer of few microns thick at the surface and

Ferrite and pearlite at the core.

Applications: These are used where a hard case and a tough core is required. Boring bits etc


I Sem

RESULT: Hence identified the different phases and obtained and draw the structures of the alloy steels.

5. REVIEW QUESTIONS: i. Why alloying elements are added to steels?

ii. How negative effects of sulphur in steels will be neutralized?

iii. What is the composition of stain less steel?

iv. What are the important characteristics of Tool steels?

v. What is the composition of H.S.S?

vi. What makes High Carbon high chromium steel suitable for making dies?

vii. Show the heat treatment cycles, on Time – temperature diagrams for different types of

steels?

viii. Compare the properties of alloy steels with and without heat treatment.


Experiment: 5.Different from JNTU SYLLABUS

STUDY OF MICROSTRUCTURES OF ALLOY STEELS

This is the first lesson in a set of images that I made that demonstrate metallurgical

microstructures of low alloy steels that are in the specimen collection. These microstructures

are shown to be sensitive to the processing and environmental history of each macrosopic

specimen. Steel usually consists simply of ferrite and cementite. The former is ductile and

soft, the latter is hard and brittle. The amount of cementite varies from nearly zero up to as

much as 15% by volume. The cementite can be either the continuous phase or it can be

present as isolated islands. Cementite can vary in size from a couple of hundred nanometers

(10^-9m) to hundreds of micrometers (10^-6m) ... a range of three orders of magnitude. The

strength (and inversely, the ductility) can vary by about half of that ... a factor of fifty or so.

Even the arrangement of the cementite can be crucial. Local or macroscopic variations in

carbon and alloy contents cause further purturbations in properties.

1. Austenitic steel

The first specimen in this lesson, which has 1.34% carbon, and which was slowly cooled

from the all austenite region of the iron-cementite phase diagram, consists of pearlite

delineated by a network of cementite. There are also Widmanstaetten cementite

platelets crossing the interiors of the larger prior austenite grains.

The first photomicrograph at left was taken at 200X; the one below it was made at

500X. A Nital etch was used.


Q. How is the prior austenite grain size indicated, why is it not uniform, and why does

the Widmanstaaetten cementite form mainly in the larger austenite grains ?

Think about your answers for a while and then take a look at the

Explanation: This is a hypereutectoid steel. During the (incorrect) slow cool from the all

austenite region, cementite precipitated, mainly at the austenite grain boundaries,

decorating them during passage through the austenite plus cementite two phase field of

the iron - cementite phase diagram. The austenite grains were of nonuniform size

because of discontinuous grain growth; small impurity particles stopped normal grain

growth by pinning the austenite grain boundaries until excessive heating permited some

of the particles to dissolve. Thereafter, a few austenite grain boundaries broke free of

the remaining particles, consuming most of the remaining austenite grains. Carbon

could not diffuse out of the centers of the larger austenite grains to join the cementite

forming at the grain boundaries during the subsequent cooling, so cementite platelets

grew inwards from the grain boundaries in order to consume the excess carbon in the

grain interiors. Proeutectoid cementite like that seen here can be distinguished from

proeutectoid ferrite because the cementite at the prior austenite grain boundaries is

continuous with the minority phase (also cementite) in the pearlite. Cementite is a

different color than ferrite, a faint lemon yellow instead of off white grey in the case of

ferrite. For a hypoeutectoid steel, the ferrite at the prior austenite grain boundaries

would be continuous with the majority phase in the pearlite.


2. Cutting tool This high carbon tap was first roll threaded and then heat treated by oil quenching from

790C. It is shown here at 200X magnification; a Nital etch was used.

The image is not terribly clear; the less decarburized metal is to the right of the bright

patches of ferrite. There are more cementite particles at the right than in the middle,

next to the ferrite patches.

What is wrong with this cutting tool ?

Explanation: This is a case of extreme decarburization. There is ferrite at the surface,

and then a carbon gradient in the martensite formed from what had been austenite plus

cementite. The decarburization occurred after the threading operation, during the

austenitization. Note that there is a discontinuity in carbon content at the ferrite - prior

austenite phase boundary, exactly as dictated by the iron - cementite phase diagram.

The ferrite deformed severely when an attemp was made to use this tool; that is why the

usual familiar tooth shape is now quite unclear.


3. Leather cutting knife

This is a transverse section of a leather cutting knife shown at 500X with a Nital etch.

The edge became bent because of excessive amounts of soft retained austenite.

The alloy is 1% carbon, 1% manganese, and 0.4% molybdenum, which is known as a

"nondeforming" tool steel. 'Nondeforming" is usually meant to mean that it won't

change dimensions during heat treatment.

The microstructure consists of tempered martensite plus about 40% retained austenite,

ten times as much as would ordinarily be tolerated. The retained austenite is not very

strong, but when it transforms to martensite during use or during a subsequent heat

treatment, the steel can crack or become embrittled. The start and finish temperatures of

the athermal transformation of austenite to martensite in plain carbon steels are quite

sensitive to the carbon content of the austenite. Austenite with more than about 0.8%

carbon will not transform completely to martensite if the austenite is only quenched

down to room temperature.

Can this knife be reclaimed ?

How would future trouble be prevented ?

Remedies: You could either convert the retained austenite to bainite by a prolonged low

temperature tempering treatment, or you could refrigerate the specimen well below the

martensite start temperature of the remaining austenite and then retemper. The

preventative treatment is to reduce the austenitization temperature of the tool to lower

the carbon content of the austenite.

Why is this possible ? Think about it, and then proceed.

http://www.georgesbasement.com/Microstructures/LowAlloySteels/Lesson-2/Specimen03.htm#Specimen_explanation


Explanation: The iron - cementite phase diagram shown here has been annotated to

indicate the carbon contents of the microconstituents of one hypereutectoid steel (i.e.,

like the present one) or one hypoeutectoid steel (like a so-called dual phase steel).

Partial austenitization causes partitioning of the carbon (along a tie line) between the two

phases of the austenite plus cementite alloy or the austenite plus ferrite alloy.

Note: Next time, refrigerate this knife immediately before tempering, temper, refrigerate

again, and retemper. This is the preferred treatment for eradicating retained austenite.

However, it only works for properly heat treated steels.


I Sem

4. High speed steel

It has unusually high resistance to softening at temperatures up to 600C. It has what is

called, red hardness. The steel is hardened by quenching austenite to martensite and

then precipitating alloy carbides at about 550C. These alloy carbides are far more

resistant to coarsening at that temperature than is cementite.

The microstructure consists of undissolved excess carbides in a matrix of artensite. These

carbides are probably the types M6C (where M is either molybdenum or tungsten) and

anadium carbide (VC). If it were tempered at about 550C, the martensite would contain

very finely divided M2C (M is again molybdenum or tungsten) which is the carbide

responsible for the secondary hardening of high speed steels. The present microstructure

is a good one, very fine grained. Note that the prior austenite grain boundaries are

delineated by the excess carbides. Below is a summary of the types and roles of carbides

in high speed steel.


I Sem

5. Stainless Steel

The specimen at left is an austenitic stainless steel containing 18% chromium, 8% nickel,

and a trace of almost unavoidable carbon as an impurity. The magnification is 500X,

and the microstructure has been made visible by etching electrolytically in an oxalic acid

solution. Stainless steels are those that have more than 12% chromium, which permits a

passive layer of either chromium oxide or adsorbed oxygen to form, preventing access of

further oxygen to the iron atoms. The rate of corrosion in aqueous solutions and the rate

of oxidation at elevated temperatures in oxidizing atmospheres are thereby greatly

reduced. Since chromium stabilizes BCC ferrite, which has marginal mechanical

properties, nickel is usually added to make FCC austenite the preferred phase.

Inadvertent slow cooling after an annealing treatment permitted chromium carbide

(Cr4C) to precipitate in this specimen on the austenite grain boundaries, where diffusion

of carbon is very fast. The austenite next to these grain boundaries has been depleted of

the chromium that went into the Cr4C, and so the metal next to those grain boundaries

is no longer stainless.

Metallurgy and material science Laboratory Manual

Exercise-6: ACCORDING TO JNTU SYLLABUS

STUDY OF MICRO STRUCTURE OF SOME NON FERROUS ALLOYS

1. AIM: To determine the phases present and to draw the microstructure of some Non ferrous alloys.

2. APPARATUS AND SPECIMENS REQUIRED: Metallurgical microscope, specimens of α – brass, α - β- brass, Gunmetal and Tin based

babbit.

3. THEORY:

3.1 Brasses: Brasses are the alloys of Copper and Zinc. From the copper-zinc equilibrium diagram shown

in fig. One can observe that the region of α – solid solution is quite wide extending from 0 to

38% of Zinc. If Zn percentage is more than 38% a second solid solution β is formed. With

zinc content more than 50% another solid solution called gamma is found. Useful Cu-Zn

alloys are those that contain less than 40% Zn.

Different brasses are Cap copper(contains 2 to 5% zinc), Gilding metals (contains 5 to 15%

zinc) Cartridge brass(70% copper, 30% zinc), Admiralty brass(69% copper, 30% zinc,1% tin),

Muntz metal(60% copper, 40%zinc), Naval brass(60%copper, 39% zinc, 1% tin).

3.2 Copper-Tin Alloys:- Alloys containing principally copper and tin are called Bronzes. Bronzes posses desirable properties of strength, wear resistance and salt water corrosion resistance. From Copper-Tin equilibrium diagram shown in fig.7.2 one can observe that the solubility of Tin Copper is

13.5% at 7980C, and it increases to 15.8% at 586

0C, and remains constant up to 520

0C,

decreases to 11% at 3500C and to about 1% at room temperature. With larger proportions of

Tin the hard compounds like Cu3Sn, epsilon phase, may appear in the structure. Useful

engineering alloys in this system are those containing less than 20% Tin. General range of composition of bronzes with respect to Copper and Tin content may be

divided into four groups as follows.

a. Alloys containing up to 8% Tin which are used for sheets and wires.

b. Alloys containing Tin percentage between 8 to 12, which are used for gears and

other machine parts. c. Alloys containing between 12 and 20% Tin which are used for bearing. d. Alloys containing between 20 and 25% Tin which are used for bells.

4. The microstructure of following specimens are observed in this exercise.

a. Cartridge Brass (α Brass): Specimen : Cartridge brass

Composition : 70% Cu, 30% Zn

Heat treatment: Nil

Etchant : Ferric chloride


The microstructure shows single phase α – solid solution of zinc in copper, grains of α – phase

are polygonal and grain size is mixed


I Sem

Application: Used for cartridge cases, radiator fins, rivets etc.

b. Muntzmetal (α - β Brass): Specimen : Muntz metal

Composition : 60% Cu, 40% Zn

Heat treatment: Nil



The microstructure shows two phases. White α – phases (α- solid solution of Zn in copper) is

present in the matrix of dark β- phase (β-solid solution of Zinc in Copper)

Applications: Utensils, Shafts, nuts, bolts and condenser tubes.

c. Gun metal: Specimen : Gun metal Bronze

Composition : 10% Sn, 2% Zn, Balance is Copper



The microstructure shows heavily cored dendrites and islands of (α+δ) eutectoid.

Applications: it is widely used for gun barrels, marine parts, valve bodies, bearing bushes etc.,

d. White metal alloys (Babbits): Babbits are either Lead based or Tin based alloys. Both the types contain Antimony. These are

mainly used as bearing materials. The microstructure of babbits consists of hard cuboids of (

Sn-Sb) in a soft matrix of eutectoid. In addition to above cuboids the microstructure may

consists of hard needles of CuSn and hard star shaped crystals of Cu3Sn.

Specimen : Tin Base Babbit

Composition : 84% Sn, 7%Cu, 9%Sb

Heat treatment: Nil

Etchant : Ferric chloride solution


The microstructure shows star shaped Cu-Sn compound. Rectangular crystals of Sn-Sb

compound are observed in ductile matrix of Cu- Sn- Sb ternary eutectic.

Applications: Bearings.

RESULT: Hence determine the different phases and obtained and draw the microstructures of some non

ferrous alloys

Metallurgy and material science Laboratory Manual 5. REVIEW QUESTIONS: i. What are the important alloys of Copper & Zinc?

ii. What is composition of Muntz metal?

iii. What is the composition of Cartridge Brass?

iv. What is a Bronze?

v. What is composition of Gun metal?

vi. What are the important applications of Gun metal?

vii. What is a Bell metal?

viii. What is melting point of Tin?

ix. What is use of Babbit metals? Explain why?

x. What is the microstructure of Tin based Babbit?


Exercise-6: DIFFERENT FROM JNTU SYLLABUS

STUDY OF MICROSTRUCTURES OF NON FERROUS METALS 1. AIM: To determine the phases present and to draw the microstructure of Leaded Brass, Phosphor

Bronze, Manganese bronze

2. APPARATUS AND SPECIMENS REQUIRED: Metallurgical microscope, specimens of Aluminum, Copper and Magnesium.

3. THEORY: 3.1 INTRODUCTION TO NON FERROUS METALS Non ferrous metals don’t contain iron as base. A wide range of non ferrous metals are

employed for various engineering applications. Most Non ferrous metals posses good

corrosion resistance, formability, castablity and special electrical and magnetic properties.

Important Non-ferrous metals, their melting points and crystal structures are tabulated here

under.

The microstructure of following specimen are studied in this experiment.

Experiment 1

Leaded Brass: NominalComposition:

Cu 59.0-64.0, Zn 34.5-40.0, Pb 0.8-1.4, Fe 0.10

Leaded Brasses

Overview Lead brasses are used for their high machinability and atmospheric corrosion resistance. The

machinability of brassis increased by the addition of lead because it acts as a microscopic chip

breaker and tool lubricant. The leadedbrasses are used for copper base screw machine

material. The alloys have excellent machinability, good strengthand corrosion resistance. Lead

can be added to any brass to increase machinability and provide pressure tightnessby sealing

the shrinkage pores. There are low, medium and high leaded brasses, with lead contents up

to 3.5%. Thelead brasses are used for architectural hardware, general purpose screw machine

parts, screws, valves, fittings,bearings and specialtyfasteners. The wrought lead brasses are designated byUNS

C31200throughC38500.Thecast lead brasses are grouped with their unleaded counter parts, and fall

in the range of alloys between C83600through C97300.The microstructure of the leaded brasse


is similar to that of the unleaded brasses. The microstructure of the leadedbrasses contain

discrete lead particles primarily in the grain boundaries or inter-dendritic regions. Lead

is practicallyinsoluble in solid copper and is present in the cast and wrought materials as

discrete particles that appear dark inthe structure. The microstructure of the as cast lead

brasses is a function of the zinc content. The lower zinccontaining alloys are single phase solid

solution alpha dendrites, with lead particles dispersed throughout theinterdendritic regions.

Those with a higher zinc content have a two phase structure, consisting of alpha and beta.The

higher zinc containing alloys have a microstructure of all beta. The lead appears as discrete

particles, appearingdark in the microstructure.

The microstructure of the wrought low zinc leaded brasses consists of twinned grains of alpha

with lead particles throughout the matrix. The higher zinc containing alloys contain a mixture

of alpha and betaphases and lead particles

Experiment 2

Phosphor Bronze

Phosphor Bronzes, or tin bronzes, are alloys containing copper, tin and phosphorous. The

phosphor bronzes containbetween 0.5 and 11% tin and 0.01 to 0.35 % phosphorous. The

addition of tin increases the corrosion resistanceand strength of the alloy. The phosphorous

increases the wear resistance and stiffness of the alloy. The phosphor bronzes have superb

spring qualities, high fatigue resistance, excellent formability and solderability, and

highcorrosion resistance. They are primarily used for electrical products, other uses include

corrosion resistant bellows,diaphragms,andspringwashers.ThephosphorbronzesaredesignatedasUNSC50100

throughC54200.Leadedphosphor bronzes combine good strength and fatigue resistance with good

machinability, high wear resistance andcorrosion resistance. They are used in applications

such as sleeve bearings, thrust washers, and cam followers.

The microstructure of wrought phosphor bronzes contain the twinned grains typical of copper

alloys. The tin remainsin the alpha copper solid solution. The phosphorus forms a copper phosphide phase. The

phosphor bronzes have awide freezing range and extensive segregation of the alloying occurs on

Alloy Family:

Phosphor bronze NominalComposition:

Cu 97.5-98.5, Sn 1.0-1.7, P 0.03-0.35, Zn

0.30, Fe 0.10,Pb, 0.05


cooling. The material that cools first aredendrites of the copper rich alpha phase. The dendrites

are heavily cored, or contain a range of compositions over their thickness. The second phase to

form is tin rich, initially transforming to beta, and finally to a mix of alpha anddelta. The alpha

and delta phases form in between the dendrites.The phosphor rich phase solidifies last as

theeutectic composition of copper phosphide. The dendrites are broken up during working and annealing, the

resultingstructure consists of grains of alpha copper and are of the alpha and tin rich delta

phases, and copper phosphide.

Experiment 3: Manganese bronze

The photomicrograph at left, shown at 100X, is of a manganese bronze composed of

copper, 39% zinc, 1.5% iron, 1% tin, and 0.1% manganese.

photomicrograph of the same specimen, shown at 500X.

The blue "stars" are an iron-zinc compound; they are a distinguishing characteristic of

this alloy.

It's been cast. The colors were not quite true in the original slides, so I adjusted the color

balance of each image. In the original specimen the beta matrix was yellow, with pink

islands of alpha; the digitally enhanced images approximate these colors fairly well, but

the "stars" now have an exaggerated blue color. The few shrinkage pores and the

absence of annealing twins pin down the "as cast" conclusion.


Exercise – 7

JOMINY END QUENCH TEST

1. AIM: To determine the hardenability of a given steel.

2. APPARATUS: Jominy test apparatus, furnace, Rockwell hardness tester and a grinder.

3. THEORY; Jominy end quench test is used to determine hardenability of steels. The process of increasing

the hardness of steel is known as Hardening. Specific specimen with standard dimensions,

used for the test is given in fig.8.1. The hardness of hardened bar is measured along its length.

3.1 Hardenability: The depth up to which steel can be hardened is defined as hardenablity. A steel having high

hardness need not have high hardenability. Hardenability may be defined as susceptibility to

hardening by quenching. A material that has high hardenablity is said to be hardened more

uniformly throughout the section that one that has lower hardenability.

M.A Gross man devised a method to decide hardenablity.

3.1.1 Critical diameter: The size of the bar in which the zone of 50% martensite occurs at center is taken as critical

diameter. This is a measure of harenablity of steel for a particular quenching medium

employed.

3.1.2. Severity of Quench: The severity of quench is indicated by heat transfer equivalent.

H = f/k

f = Heat transfer factor of Quenching medium and the turbulence of the bath.

k = Thermal conductivity of bar material.

The most rapid cooling is possible with severity of quench as infinity.

3.1.3 Ideal Critical Diameter; The hardenbility of steel can be expressed as the diameter of bar that will form a structure

composed of 50% martensite at the center when quenched with H = infinity. This diameter is

defined as ideal critical diameter.

4. Description of Apparatus: Jominy end quench apparatus is shown in fig 8.2.

The apparatus consists of a cylindrical drum. At the top of the drum provision is made for

fixing the test specimen. A pipe line is connected for water flow, which can be controlled by

means of a stop cock.

42


I Sem

5. PROCEDURE:

a. Out of the given steel bar, the standard sample is to be prepared as per the dimensions

shown in the fig.

b. The austenitising temperature and time for the given steel is to be determined depending on

its chemical composition.

c. The furnace is setup on the required temperature and sample is kept in the furnace.

d. The sample is to be kept in the furnace for a predetermined time (based on chemical

composition of steel) then it is taken out of the furnace and is kept fixed in the test apparatus.

e. The water flow is directed onto the bottom end of the sample. The water flow is adjusted

such that it obtains shape of umbrella over bottom of sample.

f. T he quenching to be continued for approximately 15 minutes.

g. A flat near about 0.4 mm deep is grounded on the specimen.

h. The hardness of the sample can be determine at various points starting from the quenched

end and the results are tabulated.

i. The graph is plotted with hardness values versus distance from quenched end. From the

results and graph Plotted the depth of hardening of the given steel sample can be determined.

6. PRECAUTIONS: 1. The specimen is to be handled carefully while transferring from furnace to test apparatus.

2. Proper water flow (at high pressure) over the bottom end of specimen is to be ensured.

7. RESULTS: Hence determine the hardenability of steel.

8. REVIEW QUESTIONS: i. What is the difference between Hardness & Hardenability?

ii. What is severity of quench?

iii. What is critical diameter?

iv. What is the ideal critical diameter?

v. What is the quenching medium employed in the test?

vi. What are the important precautions to be observed in the test?

vii. Why a flat is to be ground on the test specimen?

viii. What is the equipment used to measure the hardness of specimen in the experiment?

43

Documents

St.MARTIN’S ENGINEERING COLLEGE - SMECsmec.ac.in/sites/default/files/lab1/MMS MANUAL LAB.pdfSTUDY OF MICROSTRUCTURE OF SOME NON- FERROUS ALLOYS 36 7. JOMINY END QUENCH TEST 42 Metallurgy